Common applications for a.c. capacitor circuits include startup and operation of split-phase induction motors. In such applications, a starting winding is normally used to series-connect an electrolytic capacitor of a type suitable for a.c. operation. Electrolytic capacitors of said type are capable of sustaining only momentary loads and consequently, their use is limited to startup. In the event that the starting winding is to be connected in series with a capacitor during operation as well, the electrolytic capacitor serving as a startup capacitor must be supplemented by an additional metal foil and paper or other type capacitor which is suitable for continuous a.c. operation. Such capacitors at the capacitance values and operating voltage values required are very costly.